1. Field of the Invention
The present invention relates generally to electrical circuits, and more particularly but not exclusively to active clamp flyback converters.
2. Description of the Background Art
Flyback converters are widely employed in switched mode power supplies, including those for travel power adapters, chargers, computers, and other applications. Generally speaking, in a flyback converter, a power switch is closed to allow the primary winding of the transformer to receive an input voltage. Closing the power switch increases the primary current and magnetic flux, stores energy in the transformer, and induces current on the secondary winding of the transformer. The induced current on the secondary winding has a polarity that places a diode rectifier in reverse bias to block charging of an output capacitor. When the power switch is opened, the primary current and magnetic flux drop, and the resulting induced current on the secondary winding changes polarity to thereby forward bias the diode rectifier and allow charging of the output capacitor to generate a DC output voltage. A load is connected to receive the output voltage.
A flyback converter may incorporate a clamp to reduce voltage and current stress on its switching components. An active clamp flyback converter is a flyback converter that has an active clamp. In contrast to a passive clamp, an active clamp has a clamp switch (also referred to herein as “high-side switch”) that is switched to reduce stress on the power switch (also referred to herein as a “low-side switch”).